Concretes Using Modified Mineral Extenders

Abstract:

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The possibility of modification of mineral extenders with a specific surface of 350 m2/kg with ultraviolet irradiation is considered. Infrared spectroscopy confirmed that under the influence of ultraviolet irradiation, the bonds of OH-groups with SiO2 tetrahedra are weakened, that contributes to the formation of extenders of the acid centers of Lewis and Bronsted on the surface. The optimum time of ultraviolet exposure is determined, at which the concentration of active Lewis and Bronsted acid sites on the extenders surface increases by more than 100%. It was found that replacing 10% of cement mass with a modified extenders makes it possible to produce concretes with strength values 20-30% higher than for composites without extenders. Obtaining equal strength concrete is possible with replacing 20% of cement with modified extenders.

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V. V. Yadykina. Managing the processes of formation and the quality of construction composites given the state of the surface of the particulate material: Publishing House of the DIA, (2009) p.374.

Abstract: Waste sludges produced from the recycling of concretes contain a large amount of aggregate powders and pre-reacted cements so that they have no more cementing properties. However, since they contain unreacted Ca(OH)2, pozzolanics such as blast slag or meta kaoline can activate the waste concrete, and they can be reused as low-grade cement or pozzolanics. When meta kaoline was added with some other pozzolanic materials such as gypsum or blast slags, the density was increased so that the compressive strength, especially early stage of curing
time, was enhanced. When meta kaolin was added, more densified C-S-H gel networks were formed at aggregates, and ettringites were produced between the C-S-H gel networks.

Abstract: Different solid waste and their autoclaved waste samples were studied with the methods of infrared spectra (IR), X-ray diffraction (XRD) and chemical analysis. The results indicate that there is significant difference for strong absorbance Si-O bonds stretching vibration band of solid wastes infrared spectrum. The silicates have reacted and formed new hydrates which correspond to the strong absorbance Si-O bonds stretching vibration band. For containing activity crystal or amorphous which have ever been high-temperature heat such as fly ash, slag, waste glass and steel-slag, bound water amount of their autoclaved samples are related to strong absorbance Si-O bonds stretching vibration band, but there are no unity rules between the compressive strength of the autoclaved samples and strong absorbance Si-O bonds stretching vibration band because their type of hydrates products are significant differences. The IR characteristic peaks of waste concretes are almost same, and there are similar hydrate products (tobermorite and C-S-H (I) gel) and maximum compressive strength for different samples.

Abstract: In precast concrete elements manufacturing, steam-cured concrete incorprating 30% mineral admixtures encountered the problem of too low demoulding compressive strength. To resolve it, this paper mainly studied the influence of mineral admixtures on the compressive strength, the tensile-splitting strength and the flexural strength of the steam-cured concrete. The experimental results indicated that, compared with steam-cured concrete incorprating mineral admixtures, the later strength of steam-cured concrete incorprating 0% mineral admixtures has lower increment degree and its increment of tensile-splitting strength and flexural strength inverted to some extent. The demoulding compressive strength is too low for the high volume fly ash concrete mixtures. The problem of too low demoulding compressive strength is solved by incorprating composites of ground blast furnace slag(GBFS) and fly ash. Different varieties of mineral admixture used in the concretes can produce a certain degree of potentiation.

Abstract: Aiming at preparing the high performance concrete with metakaolin (MK) replacing silica fume (SF), comparison of fluidity between MK concrete and SF concrete was investigated in this paper. Slump, spread, and slump loss with time of fresh concrete under the condition of superplasticizer adding were tested, which containing with 5 to 15 wt. % replacement of MK, SF, combination of MK and ground granulated blastfurnace slag (GGBS), or combination of SF and GGBS, respectively. The mechanism for exploring fluidity difference of MK concrete and SF concrete were researched by measuring ζ potential and superplasticizer adsorption. The results indicate that concretes containing with 5 to 15 % MK were provided with better workability than concretes with SF. Fluidity of MK concretes incorporating with 5 to 15 % GGBS was better than that of SF concretes. Incorporating with 5 to 15% replacement, MK-cement-superplasticizer system present higher ζ potential, and lower superplasticizer adsorption than SF-cement-superplasticizer, which is an answer to why MK concrete has better fluidity than SF concrete. Physical filling effect of mineral additives is also is helpful to concrete fluidity.

Abstract: This paper carried out experiments to investigate the change of water absorption gradient of standard curing concretes and steam-cured concretes cured at 60°C. The effect of steam curing on concretes water absorption was evaluated, and the corresponding mechanism was also discussed. Results indicate that the change of water absorption gradient of standard curing concretes is non-significant with the change of the specimen height; Steam curing has exacerbated the inhomogeneity between the top surface and interior surface of concretes. It is observed that noticeable gradient difference in aborption characteristics between top, the second (1cm below top surface) and the third (3cm below top surface) surfaces of samples. Top surface absorption capacity has been the highest, and the second surfaces are in rather good accordance with the third surface. Thus the effect depth of steam curing is near to the concrete open surface. The addition of silica fume to a concrete decrease the water sorptivity of steam curing and standard curing concretes, but for the improvement of the uniformity of concrete, the effect is not markedly obvious.